Generally, a rear seat backrest is provided with a fixation wall fixed to the rear seat, and an upper back panel attached to the fixation wall. The upper back panel is a panel dividing a cabin and a luggage space and extending substantially horizontally.
Patent Document 1 describes a bead which is formed at the center in the width direction of the upper back panel and extended in a vehicle longitudinal direction to suppress a vertical vibration of the upper back panel. According to its technology, the vertical vibration of the upper back panel in the vehicle can be suppressed effectively.